Semiconductor circuits are initially manufactured as wafers. A circular wafer of a semiconductor material such as silicon is formed with a plurality of individual circuits each of which is called a die (pl. dice). After the dice are formed on the wafer, the wafer is cut so as to separate the dice from each other and each die is then assembled into a semiconductor package with bond wires connecting the bond pads of a die with the pins of the package. A number of tests on the dice are carried out at various stages in the process. In particular, for example, a test of the devices while they are still part of the wafer is carried out. This test is known as a wafer test and is used to discard dies that have been incorrectly formed.
Once the die is assembled in a package it is tested again to ensure that the package has been properly assembled and that no damage has occurred to the die during the assembly and processing and to verify that the device still meets its design specifications. This test may be carried out at several different temperatures to check parameters that may be temperature sensitive. For example commercial devices may be tested at 0° C., 25° C. and 70° C. Devices intended for military applications may be tested at more extreme temperatures still, for example −55° C., 25° C. and 125° C.
In summary, the testing of semiconductor devices is an important part of the manufacturing process, and in order to prevent the processing time being seriously delayed, methods and apparatus need to be designed that facilitate the testing of such semiconductor devices in the most time-efficient and reliable manner possible.